The modulated reflected and nonreflected light fluxes, measured as the azimuth of incident linearly polarized light is varied, yield the absolute reflectances Rp, and Rs, of a dielectric or semiconductor surface. Application to a reflective Si detector determines the refractive index and thickness of a SiO2 film on the detector surface.
R. M. A. Azzam, "Polarized light reflectometer," Appl. Opt. 33, 6009-6011 (1994)